Technical Field
The present invention relates generally to data networking and communication circuits.
Description of the Background Art
Networking switch cards, networking line cards, and blade computers communicate via electrical backplanes. The electrical signaling across these backplanes often needs to employ transmit equalization, also called pre-emphasis or de-emphasis, for the communication to be reliable. Depending upon which slots the cards are located and which cards are connected together, the transmitter equalizer settings require different values, or tap coefficients, for proper communication.
Many of the devices sold today have a 3-tap transmitter (TX) linear equalizer while some newer devices have transmitters with 4-tap TX equalizers. The main tap usually has 64 settings, while the post-tap and pre-tap generally have somewhat less adjustability at 32 and 16 settings, respectively.
Blade server manufacturers characterize each device in each slot for each setting to find appropriate values for all configurations. When a new card is inserted into the server, the system management software must have knowledge of the card and the equalizer settings for proper operation.
To enable greater interoperability between card manufacturers, server system manufacturers, and component/device manufacturers, different standards bodies have created automatic link training protocols. The link training protocols, also called auto-negotiation or dynamic equalization or protocol training, allow the devices and cards to exchange information and issue commands to each other.